Electron Deficiency in Tetrahedral Transition-Metal Clusters: Electronic Structure and Magnetic Properties of [Ru4((eta)6-C6H6) 4((mu)3-H)4]2+

Analysis of the electronic structure of the electron-deficient cluster cation [Ru4((eta)6-C6H6)4H4]2+ (1 2+) by density functional theory calculations shows a very small energy gap (0.06 eV) between the diamagnetic singlet state and the paramagnetic triplet state, as a consequence of the absence of a significant Jahn-Teller distortion in the molecular structure of 1 2+. Magnetic measurements of [1]Cl2, [1][BF4]2, and [1][PF6]2 show 1 2+ to be diamagnetic in the fundamental state, with some weak temperature-independent paramagnetism, depending upon the nature of the counterion.